BERLIN (AP) -- Facing a surge of right-wing extremism among fans, the soccer club Borussia Dortmund has long used social workers at games to defuse tense situations and help promote tolerance.

This month, however, the social workers were attacked by a group of neo-Nazi fans. One of them was beaten badly in a stadium bathroom.

It was one of many recent episodes underlining how Germany - and Dortmund in particular - is still dealing with grim reminders of its dark days of racism, intolerance and violence.

Far-right extremists in the west German city of 600,000 have infiltrated some of Borussia Dortmund's rabid fan groups. They are recruiting sympathizers, leading to more thuggery and violence.

Dortmund, in the heartland of the industrial Ruhr area, is a magnet for immigrants from all over the world. It also serves as a focal point for neo-Nazis in the state of North Rhine-Westphalia. In no other German state are more right-wing offenses recorded.

Media reports suggest about 100 neo-Nazis regularly attend games among 24,500 fans on the south terrace, Europe's largest standing-only section, in Dortmund's Westfalen Stadium.

"We believe there are a few right-wing extremists," the club said in a statement. "The authorities say they have not noticed a significant increase in their numbers in recent years. However, there have been significant changes in the type of incidents."

It may be a fringe group, but violence has increased dramatically.

Before Dortmund's Champions League game at Shakhtar Donetsk on Feb. 13, fan representative Jens Volke was accosted and struck in the face when he approached three neo-Nazis who were chanting far-right slogans.

Two of the men then followed Dortmund Fan Project leader Thilo Danielsmeyer to the toilet. The door burst open, and as Danielsmeyer turned around, he was struck in the face. An accomplice kept watch while the beating continued. The assailant kept punching him, kicking him in the back, before trying repeatedly to bash his head against the wall.

The three hooligans have been identified by the club and banned from stadiums across Germany. Each faces charges of causing grievous bodily harm and verbal abuse.

The club has pledged "zero tolerance" for right-wing extremism but faces an escalating struggle as neo-Nazis answer with displays of defiance and violent acts of reprisal.

Danielsmeyer was a logical target. The Dortmund Fan Project was founded in 1988 to combat xenophobia and racism, while promoting a message of tolerance and inclusion to troubled young men.

Lately, however, members have drifted from the group and become more receptive to far-right ideology - and to violence.

Rioting between Ruhr rivals Dortmund and Schalke last October was the worst in the area in years. In all, 180 arrests were made and 11 people were injured, including eight officers. Fans had the "potential for violence not seen for a long time," Dortmund police spokesman Michael Stein said.

And they're being urged by an older generation of violent fans who were at the center of the rise of hooliganism in the 1980s.

Better known as SS-Siggi, Borchardt helped form the infamous Borussenfront group of hooligans in 1982. It became notorious for brawling after matches and targeting Turks in Dortmund's north inner city.

The 59-year-old Borchardt has served prison terms for assault, incitement to hatred and disturbing the peace. He is no longer involved firsthand in any violent activities, with a new generation of neo-Nazis having taken over.

Borussenfront members are banned from Bundesliga games, but they meet at lower-division games and have been able to spread their right-wing ideology among other fan groups. Beer, soccer and a common enemy in rival fans or the police help lay the foundations.

Members of the Desperados group of ultras and others, such as the Northside group, have become more extreme in recent years. They now meet with Borussenfront members to train for street battles.

"There has long been the second and third generation," Borchardt said.

While membership in neo-Nazi groups has dropped in Germany, the number of far-right extremists prepared to use violence has grown, the country's domestic intelligence agency found last year.

Dortmund's neo-Nazis have become more prominent since Interior Minister Ralf Jaeger banned the violent far-right National Dortmund Resistance group last August. Members of the NWDO often overlap with those of the Desperados, Borussenfront or Northside ultras, and they have taken their protest to the stands.

A banner proclaiming "Solidarity with the NWDO" was displayed prominently during the club's opening game of the Bundesliga season Aug 24. A 27-year-old known neo-Nazi was identified and banned from all German stadiums.

Six days earlier, a banner extending sympathy to a deceased member of the "Hoonara Chemnitz" group was displayed in the Dortmund fan block at a German Cup game. "Hoonara" is an abbreviation of the words Hooligans, Nazis and Racists.

Eight neo-Nazis were banned from attending games across Germany for unfurling right-wing symbols and banners, including an imperial war flag, during a game played by Dortmund's second team at Rot-Weiss-Erfurt on Sept. 1. The Frankfurter Allgemeine Zeitung newspaper said most of them were NWDO members.

One Desperado, known to belong to NWDO, was imprisoned in September for his part in a masked-attack on left-wing youths, who were hounded out of their bus, pelted with stones and bottles and threatened with a knife.

Dortmund employs nearly 800 security officers to cover a stadium with a seating capacity of 80,720. The club has invested $330,000 in a camera system to help monitor fan behavior during games. All banners or symbols with far-right associations are banned. Fan projects are promoted and the club works closely with police and soccer authorities.

It might find out soon whether any of the measures are working - the next game between the Ruhr rivals is at Schalke on March 9.